The present invention is directed to an apparatus for measuring blood flow and, in particularly, to an apparatus which can simultaneously determine the difference in blood flow in a blood vessel at spaced locations to determine whether a partial occulsion is present and to pinpoint the location of the occlusion. The apparatus utilizes ultrasonic signals and is non-intrusive.
The Doppler effect has been utilized to provide an indication as to whether blood is flowing in a particular blood vessel. More recent prior art devices utilize the Doppler effect, which provides a change in frequency of waves emitted or reflected from a moving source such as flowing blood, to determine the velocity of flow. Such prior art devices are exemplified by U.S. Pat. Nos. 4,257,275 and Re. 28,686 which utilize two pairs of ultrasonic transducers to measure fluid flow in a vessel at spaced locations. In these patents, the signals transmitted across the fluid between the transducers of each pair are utilized to determine the time delay between the flowing material to provide a single measurement of the fluid flow velocity. Noise, frequency modulation or phase modulation in the transmitter signals are compared. Other arrangements utilizing pairs of transmitters-receivers, as exemplified by U.S. Pat. Nos. 3,977,247 and 3,766,517 provide single measurements of velocity or flow volume by focusing on the same or overlapping volumes.
None of these prior art devices are capable of determining whether an occlusion exists in a blood vessel by utilizing ,the different in blood flow speed measured at two spaced locations based on its Doppler effect. Accordingly, it is desired to ,provide a blood flow measurement apparatus which utilizes the Doppler effect to pinpoint the location of an occlusion in a blood vessel.